linux-kernel - Re: [PATCH] AB3100 regulator support v1

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Message-ID: <Pine.LNX.4.44L0.0908311623490.2646-100000@iolanthe.rowland.org>
Date:	Mon, 31 Aug 2009 16:27:51 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
cc:	Linus Walleij <linus.ml.walleij@...il.com>,
	<linux-kernel@...r.kernel.org>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Liam Girdwood <lrg@...mlogic.co.uk>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Russell King <linux@....linux.org.uk>,
	<linux-arm-kernel@...ts.arm.linux.org.uk>
Subject: Re: [PATCH] AB3100 regulator support v1

On Sun, 30 Aug 2009, Mark Brown wrote:

> On Sun, Aug 30, 2009 at 12:27:32PM -0400, Alan Stern wrote:
> > On Sun, 30 Aug 2009, Mark Brown wrote:
> 
> > > On the face of it (and without having actually looked at a running
> > > system or anything yet) I'm rather surprised that platform based MFD
> > > drivers aren't running into this issue more often.  CCing in Alan who
> > > made the change.
> 
> > I'm not at all familiar with the detailed issues involved here.  
> > Perhaps because of this, I don't see why there's any reason for
> > deadlocking.  __driver_attach() is invoked when a new driver is
> > registered; to avoid problems all you have to do is make sure you
> > aren't holding any device locks when you register a driver.
> 
> Ah, it's platform_driver_probe() that's causing issues.  When it is used
> the devices need to have been registered previously since the driver
> probe function isn't kept around.  In order to do this for the child
> device the driver for the subdevice has to be registered from within the
> probe function of the parent, which is itself happening within the
> parent device registration.

I see.  Well, in the absence of any more sophisticated solutions,
unlocking the parent's semaphore before registering the driver (and
then re-locking it afterward) should work.

Alan Stern

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